Botanical name: Fucus vesiculosus
© Martin Wall
Parts used and where grown
Bladderwrack is a type of brown algae (seaweed) that grows on the northern Atlantic and
Pacific coasts of the United States and on the northern Atlantic coast and Baltic coast of
Europe. The main stem of bladderwrack, known as the thallus, is used medicinally. The thallus
has tough, air-filled pods or bladders to help the algae float—thus the name
bladderwrack. Although bladderwrack is sometimes called kelp, that name is not specific to
this species and should be avoided.
Bladderwrack has been used
in connection with the following conditions (refer to the individual
health concern for complete information):
Historical or traditional use (may
or may not be supported by scientific studies)
Bladderwrack’s mucilaginous thallus has long been used to soothe irritated and
inflamed tissues in the body.1 It was also historically used as a bulk-forming
laxative.2 People living near oceans or seas have a historically low rate of hypothyroidism, due, in part, to ingestion of
iodine-rich food, such as seafood and seaweeds like bladderwrack. It has also been used to
counter obesity, possibly due to its
reputation for stimulating the thyroid gland. Clinical research in this area has failed to
confirm that seaweeds like bladderwrack help with weight loss,3 though more
specific research is warranted.
Active constituents
There are three major active constituents in bladderwrack: iodine, alginic acid, and fucoidan.
The amount of iodine in bladderwrack is highly variable,4 probably as a result
of different amounts of iodine in the water where it grows. A reasonable portion of
bladderwrack may contain the U.S. adult recommended dietary allowance (RDA) of iodine (150
mcg). The RDA amount of iodine is believed to be necessary for maintenance of normal thyroid
function in adults (infants and children need proportionally less). Thus, in people with
insufficient iodine in their diet, bladderwrack may serve as a supplemental source of iodine.
Either hypothyroidism or goiter due to insufficient intake of iodine may
possibly improve with bladderwrack supplementation, though human studies have not confirmed
this.
Alginic acid is a type of dietary fiber
that can be used to help relieve constipation
and diarrhea. However, human studies have not
been done on how effective bladderwrack is for either of these conditions. An over-the-counter
antacid, Gaviscon®, containing magnesium carbonate and sodium alginate (the sodium salt
of alginic acid), has been shown to effectively relieve the symptoms of heartburn compared to other antacids in a double-blind
study.5 However, bladderwrack has not been studied for use in people with
heartburn. Bladderwrack might also help indigestion, though again clinical trials have not
been conducted. Calcium alginate (the calcium salt of alginic acid) has shown promise as an
agent to speed wound healing in animal
studies6 but has not been demonstrated to be effective in humans.
Alginic acid has also been shown to inhibit
HIV in the test tube.7 However, this effect has not been studied in humans.
Alginic acid may help lower LDL (“bad”) cholesterol levels, according to animal
studies.8 No human trials have studied this effect of bladderwrack. It is widely
used in food and pharmaceuticals as a thickener and gelling agent.9
Fucoidan is another type of dietary fiber in bladderwrack that contains numerous sulfur
groups. According to test tube and animal studies, this appears to give fucoidan several
properties, such as lowering LDL cholesterol levels,10 lowering blood glucose
levels,11 anti-inflammatory activity,12 possible anticoagulant
effects,13 and antibacterial14 and anti-HIV activity.15
Though it has not been definitively proven, fucoidan is thought to prevent bacteria and
viruses from binding to human cells, a necessary step in starting an infection, as opposed to killing the microbes
directly.16 17 To date, no human clinical trials have been done with
fucoidan or bladderwrack to support their use for any of these conditions.
How much is usually taken?
For short-term use (a few days) to relieve
constipation, powdered bladderwrack can be taken in the amount of 1 teaspoon three times
per day along with at least 8 oz of water each time.18 For thyroid problems, gastritis, or heartburn, 5 to 10 grams of dried bladderwrack in
capsules three times per day has been recommended. Alternately, bladderwrack may be eaten
whole or made into a tea using 1 teaspoon per cup of hot water, allowing each cup to sit at
least 10 minutes before drinking. Three cups per day of tea can be drunk. No more than 150 mcg
iodine should be consumed from all sources,
including bladderwrack, per day.19 However, most bladderwrack products do not give
any indication of their iodine content. Therefore, anyone considering taking bladderwrack
should first consult a physician trained in nutrition and herbal medicine.
Are there any side effects or interactions?
Bladderwrack is generally safe, though there are three potential problems with its
consumption: acne, thyroid dysfunction, and
heavy-metal contamination. Iodine in any form—including from bladderwrack and other
seaweeds—can cause or aggravate acne in some people.20 Excessive iodine
ingestion can cause either hypothyroidism or hyperthyroidism and should be
avoided.21 22 Bladderwrack and other seaweeds that grow in
heavy-metal-contaminated waters may contain high levels of these toxins (particularly arsenic
and lead), leading to nerve damage,23 kidney damage,24 or other
problems. Only bladderwrack known to have been harvested from clean water or labeled to
indicate the absence of heavy metals or other contaminants should be consumed. The safety of
using bladderwrack during pregnancy and breast-feeding is unknown. People who are
allergic to iodine may need to avoid bladderwrack.
At the time of writing, there were no well-known drug interactions
with bladderwrack.
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3. Björvell H, Rössner S. Long-term effects of commonly
available weight reducing programmes in Sweden. Int J Obes 1986;11:67–71.
4. Norman JA, Pickford CJ, Sanders TW, et al. Human intake of arsenic and
iodine from seaweed based food supplements and health foods available in the UK. Food
Addit Contam 1987;5:103–9.
5. Chevrel B. A comparative crossover study on the treatment of heartburn
and epigastric pain: Liquid Gaviscon and a magnesium-aluminum antacid gel. J Int Med
Res 1980;8:300–3.
6. Barnett SA, Varley SJ. The effects of calcium alginate on wound
healing. Ann R Coll Surgeons Engl 1987;69:153–5.
7. Béress A, Wassermann O, Bruhn T, et al. A new procedure for the
isolation of anti-HIV compounds (polysaccharides and polyphenols) from the marine alga
Fucus vesiculosus. J Nat Prod 1993;56:478–88.
8. Vázquez-Freire MJ, Lamela M, Calleja JM. Hypolipidaemic activity
of a polysaccharide extract from Fucus vesiculosus L. Phytother Res
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11. Vázquez-Freire MJ, Lamela M, Calleja JM. A preliminary study of
hypoglycaemic activity of several polysaccharide extracts from brown algae: Fucus
vesiculosus, Saccorhiza polyschides and Laminaria ochroleuca.
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anti-inflammatory compounds castanospermine, mannose-6-phosphate and fucoidan on allograft
rejection and elicited peritoneal exudates. Immunol Cell Biol
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fucoidan. The interaction of fucoidan with heparin cofactor II, antithrombin III and thrombin.
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17. Lederman S, Gulick R, Chess L. Dextran sulfate and heparin interact
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20. Harrell BL, Rudolph AH. Kelp diet: A cause of acneiform eruption.
Arch Dermatol 1976;112:560 [letter].
21. Okamura K, Inoue K, Omae T. A case of Hashimoto’s thyroiditis
with thyroid immunological abnormality manifested after habitual ingestion of seaweed.
Acta Endocrinol 1978;88:703–12.
22. Kim JY, Kim KR. Dietary iodine intake and urinary iodine excretion in
patients with thyroid diseases. Yonsei Med J 41:22–8.
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